I. Field of the Invention
This invention relates generally to liquid supply apparatus for spray guns, and more particularly to an air pressure-assisted liquid supply apparatus attachable to a liquid input port of a spray gun.
II. Discussion of the Prior Art
Various liquid supply devices are known in the art for supplying mixtures of component liquids to be sprayed via air-powered spray guns, such as those commercially available from Sata Farbspritzechnik GmbH & Co., Lex-Aire Products, Inc. of North Billerica, Mass., Graco, Inc. of Minneapolis, Minn., and a model available from Wagner Spray Tech Corporation of Minneapolis, Minn.
U.S. Pat. Nos. 6,752,179, 6,796,514 and 6,953,155 each describe a cup-like assembly for feeding liquid to the inlet port of such spray guns. In each of those patented arrangements, the liquid to be sprayed is contained within a collapsible polymeric bag and the bag is, in turn, disposed in a rigid cup-like housing. An adapter designed to mate with the inlet connection of a particular spray gun is in fluid communication with the contents of the bag. When air under pressure is introduced in the space between the bag and the rigid housing, the bag is compressed forcing the liquid contents thereof out through the adapter and into the inlet port of the spray gun with which the liquid feeding assembly is attached.
In so-called “gravity-fed units”, the liquid inlet for the spray gun projects upward from the barrel of the gun and the cup assembly with its tubular adapter is inverted when joined to the gun's inlet. Gravity and/or the Venturi-effect produced by high velocity flow air through a nozzle are used to draw the liquid from the flexible bag and into the air stream ultimately exiting the barrel of the spray gun. Again, as the liquid is extracted from the flexible bag, it collapses. Here, reference is made to the Schwartz U.S. Pat. No. 6,796,514 as an example of a prior art gravity-fed spray gun.
One problem associated with gravity feed is that the spray pattern tends to be position sensitive. That is to say, when the liquid supply cup is disposed above the gun barrel, an adequate stream of liquid is drawn from the cup and mixed with the air stream to provide a full coverage pattern. However, if the shape of the object being treated, e.g. spray painted, necessitates inverting the gun such that the supply cup is disposed below the gun barrel, the suction force due to the Venturi nozzle may be insufficient to draw an adequate quantity of the liquid, creating an uneven pattern.
Accordingly, a need exists for an improved pressurized liquid supply device for use with a spray gun.